The present invention relates to compositions of mixed metal salts which exhibits improved storage stability, and to the use of such compositions as a stabilizer for polymers.
Mixed metal salts of carboxylic acids are useful for many purposes. In particular mixed metal salt of carboxylic acids having at least 6 carbon atoms have been used as industrial soaps and greases in various applications, including use as stabilizers for polyvinyl chloride and other chlorine containing polymers. Often the salts are overbased, as described hereinafter, and often such salts are used in the form of a concentrate, e.g. with an amount of oil sufficient to provide a mobile, homogeneous, pourable, and handleable material.
While such mixed salts and compositions are very useful, problems are sometimes encountered. In particular the stability of certain combinations of metal salts to standing or storage can be inadequate due to fundamental incompatibility among the metal salts employed. Such incompatibility can be exhibited in oil formulations by development over time of turbidity, increased viscosity, or insoluble solids. As a result the composition is no longer an easily-handled, homogeneous, readily pourable liquid and must be specially treated in order to be used. Even in the absence of added oil certain mixed salts can exhibit deleterious interactions. The present invention provides a composition of mixed metal salts in which such problems are minimized or completely eliminated and which, accordingly, is superior for various uses including use as a polymer stabilizer.
Various references have reported the use of carboxylate salts as polymer stabilizers, and various problems encountered therein. French publication 2,376,178, Jul. 28, 1978 discloses chemical stabilizers that protect halogenated vinyl polymers from rapid decomposition due to exposure to heat, comprising a tin complex or a complex of antimony, a hydrochloric acid acceptor, an organic chelating agent, and a lubricant. The hydrochloric acid acceptor is a salt of an alkali or alkaline earth metal or Zn, Cd, or Pb oxides, which can be cleaved by HCl. It is also possible to use superbasic salts. The organic chelating agent captures the metal chlorides produced during thermal degradation and forms stable and inoffensive complexes. Suitable agents include oxycarboxylic acids, polyols, polyamines, and organic phosphites.
U.S. Pat. No. 2,669,549, Darby et al., February 1954, discloses PVC stabilized with zinc stearate and calcium ethyl acetoacetate. The PVC is resistant to discoloration.
U.S. Pat. Nos. 4,123,399 and -400, Gay, Oct. 31, 1978, disclose a PVC formulation containing a mixed organometallic salt, a polyol, and a .beta.-diketone. The organometallic salt is e.g. calcium stearate plus zinc stearate. Other combinations include calcium or barium salts used conjointly with cadmium or zinc salts.
U.S. Pat. No. 5,102,933. Bae et al., Apr. 7, 1992, filed May 22, 1990, discloses a composition which is useful as a thermal stabilizer for PVC, comprising a substituted .beta.-diketone, mannitol, and a mixture of magnesium and zinc salts of benzoic and fatty aliphatic acids, preferably having at least 10 carbon atoms.